Tire inflation systems are becoming crucial in motor vehicles. Those systems are deeply adopted in different types of vehicles such as trucks, tractors or earth-moving machines. A main objective of a tire inflation system is to adapt the tire pressure to different operating conditions, which depends basically on the ground to be traveled as well as a speed and a load of a vehicle using the tire inflation system. A contact area of a tire is influenced by a pressure of the tire. With a low tire pressure the contact area is increased, and with a high tire pressure the contact area is decreased. For this reason, it is necessary to optimize a tire pressure depending on the ground conditions. A lower pressure is adopted for soft surfaces such as gravel, while a higher pressure is chosen when traveling on hard surfaces, such as tarmac or concrete. Moreover, appropriate tire pressure can provide enhanced tire preservation, reduced soil compaction, improved fuel consumption, and reduced overall operating costs.
FIG. 1 illustrates a central tire inflation system (CTIS) 50 that is known in the art. It is understood that the CTIS 50 is exemplary in nature, and that the CTIS 50 may be adapted through the addition or removal of components. The CTIS 50 is a system for inflating or deflating one or more tires 52, depending on a ground condition. Generally, the CTIS 50 is comprised of several components and devices, as shown in FIG. 1. An air compressor 54, which provides pressurized air, is fitted to a vehicle 56. The compressed air passes through an air dryer 58 and is stored in an air tank 60. Based on an input coming from a driver of the vehicle 56 or from an internal algorithm of an electronic control unit (ECU) 62, a pneumatic control unit 64 provides air flow to the tires 52. Each of the tires 52 is fitted with a secondary wheel valve 66 that is used to inflate of deflate each of the tires 52. The CTIS 50 also typically comprises a rotary transmission joint 68 which allows for compressed air to be transmitted from a portion of the CTIS 50 on the vehicle 56 to each of the tires 52, which are rotatably. The rotary transmission joint 68 affords fluid communication for each of the tire 52. Such a rotary transmission joint 68 typically comprises a stator structural group coupled to the vehicle 56 and a rotor structural group located on the tire 52.
Since it is desirable that the tire 52 can be inflated and deflated during operation of the vehicle 56, tire inflation systems known from the prior art comprise rotary seal arrangements which are disposed between a vehicle spindle and a wheel hub, on which the wheel and the tire are mounted. Generally, such rotary seals are the most critical devices in the CTIS 50, since they are required to transmit the fluid from the pneumatic line to the wheel valve 66 while rotating with the tire 52. These rotary seals usually include sealing means, disposed on the spindle and/or on the wheel hub, in sliding contact between each other. The sealing means, therefore, forms a dynamical annular seal chamber, through which fluid can be transported from the pneumatic control unit 64 to the tire 52 and vice versa.
In some cases, solutions of this problem have been obtained by fitting the rotary joint with special sealing means inside the axle of the vehicle. A version of this solution has been developed by DANA ITALIA S.P.A., which is described in published international patent application number WO 2013/156430 A1. This solution is particularly interesting because of its compactness and integration with the whole axle. However, such a solution requires the design of the rotatable part to be integrated with the spindle and the wheel hub. In some cases, this requires a complex manufacturing setup due to a length of the bores that have to be formed in the axle.
It would be advantageous to develop a rotary seal arrangement for a central tire inflation system that is located externally to an axle spindle that facilitates assembly of the rotary seal arrangement.